The invention relates to a method and an apparatus for handling leaves of sheet material, for instance folded signatures, which are guided successively along a conveyor path and separated into partial streams. At the end thereof they may be formed into a stack.
Known handling and stacking apparatus can generally only process one sheet size since the stack is bordered at the ends by a plate. If the size of the plate differs substantially from the size of the sheets the sheets can be damaged when tying the stack. The field of use of such systems is thus limited. Furthermore, the stacks produced are long and heavy.
It is also known to produce smaller stacks and to handle these manually. In this method the speed of handling must be extremely high since the stacks are removed from the sheets which are being continuously conveyed.
It is desirable to make a sufficient period of time available for the handling of such stacks which are formed from a continuously moving flow of sheets.
Techniques for separating a stream of sheet material into partial streams, spaced apart so that they arrive at handling stations at spaced time intervals, are known. It is well known to interpose a barrier intermittently to create gaps. But this leads to disruption of the array sheets retained by the barrier, making their subsequent handling difficult and possibly damaging them. It does not permit precise quantities of material to be separated.
U.S. Pat. No. 4265443 discloses the use of two conveyors in succession. The first is telescopic so that the location on the second conveyor where it deposits material is variable. Both conveyors are periodically accelerated and decelerated in use. Overall this is complex and inconvenient, and does not allow precise quantities of material to be separated without disruption of the array.
GB-A-2127381 discloses a signature conveyor with a continuous chain running in parallel adjacent part of its conveying run. A length of the chain bears signature engaging lugs. A group of signatures is retained by indexing the chain so that the lugs lift signatures off the conveyor. Following signatures pile up from the rear, until the chain is moved again, returning the signatures to the conveyor. This disturbs the array of signatures and does not allow precise quantities of material to be separated. GB-A-2139991 discloses a first conveyor that feeds a second conveyor. Associated with the first conveyor is a continuous loop whereof a length is thickened such that when this portion is adjacent the conveyor, it projects above the conveying surface to lift sheets off it. Initially, the conveyors and the loop are driven at the same speed. Once the thickened portion has lifted a length of signatures, the loop and the second conveyor are accelerated. Thus a batch of sheets is deposited on the second conveyor and spaced from the following sheets. This is disadvantageous in that it does not enable the batches to be precisely predetermined.